The present invention relates to a drying apparatus (equipment) for drying a powder particle such as plastic pellet, using high pressure gas, in particular, high pressure gas having a low humidity (low dew point).
Conventionally, a hopper dryer type drying apparatus has been widely known as a drying apparatus for drying a powder particle such as a plastic pellet. The drying equipment is arranged on an upper portion of an injection machine or extruder, and has a hopper receiving a plastic pellet, and a control unit which is arranged side the injection machine or extruder, and is connected with the hopper by an air supply passage and a return passage. The control unit includes a dehumidifier, a heater, a compressor, a circulating fan and the like, in its interior. Further, the control unit supplies a high pressure dry air to the hopper via the air supply passage while recovering exhaust gas after dry treatment from the hopper via the return passage, and then, dehumidifies and heats the recovered exhaust gas after dry treatment, and thereafter, again supplies the exhaust gas to the hopper via the air supply passage. In the aforesaid manner, in the drying apparatus, the exhaust gas after dry treatment is circulated, and then, is recycled, and thus, a pellet is dried. This type of control unit has been disclosed in Japanese Laid-Open Patent Publication No. Hei8-207044, for example.
By the way, a drying speed of the plastic pellet received in the hopper increases in proportion to an amount of drying air passing through the hopper. Therefore, in order to increase the drying speed of pellet, there is the need of supplying a large amount of drying air to the hopper. In order to achieve this, large-size and high performance compressor and circulating fan are required. In addition, this kind of conventional drying apparatus is constructed in the following manner; more specifically, the entire amount of exhaust gas after dry treatment from the hopper is returned back to the control unit, and then, is dehumidified in the control unit, and thereafter, is again circulated. For this reason, inevitably, the control unit must be made into a large size.
As a result, the drying apparatus is made into a large size as a whole; for this reason, there is a problem that an introduction (manufacture) cost and a running cost become high. Moreover, an installation space for the control unit must be secured; for this reason, a large-diameter air pipe (duct) is indispensable. As a result, there is a problem that a wide space is required around the injection machine or extruder, and also, a construction cost for installing the drying apparatus increases.